Method and apparatus for brightening tin plate



Jan. 11, 1949. J, 5, NACHTMAN 2,458,525

METHOD AND APPARATUS FOR BRIGHTENING TIN PLATE Filed May 17, 1943 5 Sheets-Sheet 1 I @1015 )1 Mailman $2M w Jan. 11, 1949.

J. S. NACHTMAN METHOD AND APPARATUS FOR BRIGHTENING TIN PLATE Filed May 17, 1945 5 Sheets-Sheet 2 1 (U) (OJ 7 CD 301% V Ejwucmtow Wimp Jan. 11, 1949.. J. s. NACH'FMAN METHOD,AND APPARATUS FOR BRIGHTENING TIN PLATE Filed May 1'7, 1943 5 Shets-Sheet s 1 my C3 294 1 Film V LTZZZZZZI 64- 15 Jan. 11, 1949'. I J, 5, NACHTMAN 2,458,525

METHOD AND APPARATUS FOR BRIGHTENING TIN PLATE Filed May 17, I943 5 Sheets-Sheet 4' Jan. 11, 1949. a N H N 2,458,525

METHOD AND APPARATUS FOR BRIGHTENING TIN PLATE Filed May-17, 194s.v s sheet -sheet 5 Patented Jan. 11, 1949 Marnob AND APPARATUS FOR BRIGHTEN- mo TIN PLATE John S. Nachtman; Youngstown, Ohio Application May 17, 1943, Serial No. 487,241

11 Claims.

The invention relates generally to the continuous manufacture of bright electrolytic tin plated strip and more particularly to the production of bright electrolytic tin plated strip at minimum cost and maximum eificiency.

In certain prior methods-and apparatusior producing bright electrolytic tin plate, the brightening has been accomplished by heating the strip to melt and reflow the tin coating, and then quenching the strip in cold oil to set the tin before physically contacting it with guide rolls and the like. The heating of the strip to melt the tin has been done by passing the strip through hot oil, or by high frequency induction heating, or by electric resist'anceheating. In each instance the heat for melting the tin has been supplied from an independent heat source to heat the oil, or inthe form of electric energy to the induction coil or to the strip for resistance heating; and the oil in the quenching tank has been keptcool by circulating the oil through a heat exchanger in which the excess heat absorbed by the oil is transmitted to cooling water which is discharged into a waste outlet or sewer.

Accordingly, the heat exchange in cooling the strip from melting temperature to quenching temperature is entirely wasted and represents a high loss of heat energy which makes the cost of brightening tin plated strip excessive.

The present invention provides for brightening electrolytic tin plated strip in such manner as to utilize the heat energy normally lost, for heating the strip prior to melting, thus increasing the overall efficiency of the brightening system and decreasing the cost of operating the same. I

It is therefore an object of the present invention to provide an improved method of brightening tin plated strip which reclaims the heat transmitted from the strip to the"quenching medium and utilizes said reclaimed heat for preheating the strip prior to melting the tin plating. r

Another object is to provide a an improved method of passing the outgoing strip through a quenching medium in one direction, and the incomingstrip in the same or the opposite direction through said quenching medium in close proximity to the outgoing strip, thus producing a balance of heat transfer.

A further object/is -to=provide an improved method ofbrightening utilizing the same heat conducting medium'for preheating, melting and uenching. I "Astill further object is to provide an improved 2 method of brightening including reclaiming heat transmitted from the strip to the quenching medium, which method is adapted for utilizing a variety of ways of heating the strip to a temperature sufiicientto melt the tin.

Another object is to provide improved apparatus for brightening having preheating, melting and quenching compartmentsso c0nstructed and arranged that the incoming strip passes through the quenching compartment in a path parallel to the outgoing strip but in the opposite direction thereto.

A further object is to provide an improved method of circulating heat conducting medium in and between various compartments in such a way as to maintain desired temperatures in each of said compartments.

Also it is an object of the present invention to control the temperature to which the strip is preheated just before'melting the tin, by controlling the temperature of the strip as it enters the preheating zones so as to eliminate spoilage of material if the strip is stopped or slowed up for short periods of time. a

A further object of the invention is to provide an improved method of carrying out preheating, melting and quenching operations utilizing a heat transfer medium comprising a petroleum fraction having a final boiling point range between the approximate limits of 450 F. and 850 F. f

Also it is an object of the present invention to utilize the heat used in connection with controlling the finalsurface film on the brightened tin strip to dry-or initially reheat the strip prior to entering the first liquid preheating zone.

Finally, it is an object of the present inventionto provide improved methods and apparatus which will accomplish all of the foregoing objectives and provide a novel system for brightening tin plated stripwith increased efiiciency and minimrimbost,

These and other objects are attained by the improved methods and apparatus comprising the present invention, preferred embodiments of which are shown in the accompanying drawings and described herein, the novel combinations and sub-combinations of elements and method steps embodied in the invention being defined in the appended claims.

In general terms theinvention -comprises passing the electroplated strip through a body of heat conducting medium for preheating the tin coating below 'its'meltingpoint, then raising thetemperature of the strip to melt the tin,

quenching the strip in said preheating body of heat conducting medium, whereby heat absorbed from the quenched strip is transferred through said medium to the incoming strip.

Referring to the accompanying drawings,

Figure 1 is a diagrammatic sectional view of a preferred form of apparatus for carrying out the present invention, in which the strip is heated in a .heat conducting medium for melting the tin;

Fig. 2 is a similar view of a modified form of apparatus in which the strip is heated by electric resistance for melting the tin;

Fig. 3 is a transverse sectional view of the upper guide roll in Fig. 2, showing the electrical connections thereto;

Fig. 4 is a view similar toFig. 1 of .another modified form of apparatus, in which the strip is heated by an electric induction coil for;me1tin the tin;

Fig. 5 is a view similar to Fig. 1 of a further modification of apparatus (embodying improved means for controlling the film .left on the strip after quenching; and

Fig. 6 is a view .similar .to Fig. l-ofstill another form .of apparatus in which the strip enters the heat treating apparatus .at one :side and leaves at the opposite side.

Similar numerals :refer to similar throughoutthedrawings.

The strip S, when introduced .into the novel and improved brighteningapparatus has been electroplated withtin, and.,-.preferably rinsed and dried in a conventional manner. In some cases parts the striphas beengiven anacid treatment before L at a temperature of 150 to 200 and. is immediately=-subjected .to .the brightening treatment.

Referring .first -to the form of the invention shown in Fig. l, the .novel .apparatusincludes. a brightening tank indicated generally at 6 having outer walls 1 and partition walls 8.and 9 dividing the tank into three main compartments which may be designated A, B and .0. Compartment A comprises theheat transfer .or first preheat zone. compartment -B is .the second preheat :zone,and .the upper part-of compartment C is the fusing zone, while the lower-part is the quenching zone. It will be noted that the bottom of compartment C communicates with the bottom of compartment A.

-A preferably rounded hood portion In closes the upper ends of compartments -B and C and the upper end of compartment Az-may-be open to the atmosphere as shown. :In this form of apparatus, as well as the apparatus-pf Figs. 2 :and4,

compartments A, B and C are filled to -a common level L as shown with a liquid heat transfer medium which may for-example be a high boiling petroleum fraction having-a final-boiling point range :between the-approximate limits of-450-F. and 850 F. That is .to :say, 'the final boiling point of thypetroleumfraction-shouldvnot be lower than about :450" F. and the final boilin point should not be higher than about ".850" Petroleum fractions having final iboilmgpoints within this range are contemplated; :and. such materials will not deposit a carbon smudge on the tin.

The incoming strip S from the dryer passes over a guide roll [I into and through compartment A, around guide roll 12 and upward through compartment B, then over guide roll l3 and downward through compartment C, and then under guide rolls I4 and I5 and upward through compartment :A in a path parallel .and in close proximitycto the incoming strip travelling downward or in the opposite direction to the outgoing strip.

The .incoming strip is preferably heated to a temperature of approximately F. in the drier before passing into compartment A, but this initial preheating temperature may be and preferably is varied in coordination with the strip speed so that the temperature may be reduced .in acase the strip is stopped or appreciably slowed up for a short period of time for joining successive coils end to end. .As the strip passes through compartment .A, itmis further heated from its initial incoming temperature of about 150 F. toapproximately 300 F.

The temperature .of the liquid medium in compartment B is maintained .at a temperature slightly below the melting point of tin (449.5 F.) by means of-a heating and circulating system including a suction pipe 1.6 which withdraw medium from near the bottom .of the compartment and-conveysit byzmeans of.-a pump I! through a :filter 18 to a heater l9, where it is heated and then returned through pipe 20 to sprays 2i, which spraythe hotliquid .into the medium in a direction against the strip .-near the liquid level.

A partition 22 is provided .at the bottom of compartment B for permitting passage of the strip into the compartment, while .substantially preventing circulation of the medium in B downward into the medium in compartment A.

That portion of compartment B between the partition Hand-the liquid level .L may be called the second preheating .zone, and the strip in passing through said zone heated to a temper- .ature of about 440 F.-or inother words to a temperature just below-the melting point of the tin coatingthereon.

.In passing over vroll l3, the strip is still below the melting temperature (Of tin so as not to mar the coating, and (then passes downward into compartment C, the upper partof which constitutes the zfusing zone. In this .zone the liquid medium is maintainedrat-a temperature above the melting point of tin 'by :a heating and circulatingnystem including :a :suction pipe 23, pump 24, filter 25, heater 26, return pipe 21 and sprays 2B. As the strip passes through this-fusing zone, its temperature is raised rapidly from the pre heated temperature of 440 F. to a temperature of about i460F. to melt and'flow the tin .coating.

At (the bottom of (the fusing :zone the strip passes throng-h a partition .29 similar to partition 22, and thence into the quenching zone which occupiesthe lower portion of compartment C.

:In'the quenching 'zone .thestrip is sprayed at sprays 30 'wit'hrcooled "liquid medium withdrawn from the bottom -;of the tank by pump 3|, which rapidly cool the coating to below 425 before the strip reaches guide roll 14, so that the bright mirror-like finish imparted \to the "tin by fusing is not-marred by .the guide roll.

.As the strip passes-under ,iguide roll 15 and upward :as :shown at -S through compartment A it will continue to give up its heat to the liquid medium in said compartment, and the strip emerges from the liquid in compartment A at a temperature of approximately 310 F. The liquid medium in compartment A transfers heat to the incoming strip S travelling in a parallel path in the'opposite direction through said compartment, causing a balance of heat transfer between the outgoing and incoming parts of the strip. Consequently compartment A, where the incoming and outgoing strip parts parallel each other, may be termed the first preheat zone because all of the heat given up by'the strip during quenching and while passing from the quenching zone to and through compartment A is transferred to the incoming part of the strip S to preheat the same.

Accordingly, substantially all of the heat transmitted from the strip to the quenching medium is reclaimed and utilized for preheating the strip prior to its entering the second preheat zone, so that the brightening treatment has increased efficiency and reduced cost.

In order to reduce the amount of film of heat transfer medium on the outgoing strip S" as it leaves the first preheating zone in compartment A, the strip may be passed in a compartment D between squeegee rolls 33 and 34, over roll 34 and then downwardly around a guide roll 35 submerged in a liquid medium having a. level L which is a solvent for the heat transfer medium in compartments A, B and C. This solvent may be an aliphatic or aromatic hydrocarbon such as a petroleum solvent or fraction of lower boiling point range which will act as a solvent for the higher boiling point heat transfer medium without leaving a smudge on the tin coating.

The strip passes upward from guide roll 35 between squeegee rolls 36 and 31 and thence downward in compartment E under guide roll 38 and upward between squeegee rolls 39 and 40 and out through a seal 4| into the atmosphere.

Guide roll 38 may be submerged in a bath of the solvent medium to which has been added a small amountsay about 1% by weight,of a desired oil for protecting the strip surface, so that when the strip emerged into the atmosphere, the solvent left on the strip will evaporate and leave a very thin film of the desired oil on the strip surface. This oil forming the coating on the finished strip may be the same oil as is used for the heat transfer medium in compartments A, B and C.

lhe amount of heat transfer medium carried over on the strip into the solvent bath may be controlled by a distillation system which includes a pipe 42 for withdrawing liquid medium from the bottom of compartment D to a pump 43 which forces the liquid to a distillation unit 44 for separating the two liquids. From unit 44, the solvent liquid is returned through pipe 45 and sprays 46 to compartment D, While the heat transfer liquid is returned by pipe 41 and pump 48 to compartment A.

Preferably, means for relieving pressure built up in the hood H] by vaporization of the heat transfer medium includes a condenser 50 for condensing vapor in pipe 5, carrying vapor from the hood In. The condensed vapor passes through a liquid seal 52 and is returned by a pipe 53 to the fusing compartment.

The modified forms of apparatus shown in Figs. 2 and 4 are substantially identical with that shown in Fig. 1, except for the method of heating the strip in the fusing zone to melt the tin, and the corresponding parts are numbered the same as in Fig. 1.

In Fig. 2, the strip passes over a hollow currentconducting. guide roll l3a before passing through the'fusing zone C, then through the quenching zone, and then aunder'another hollow current conducting iroll I4a, from which it passes out through-the heat transfer or first preheat compartment. Preferably, the rolls l3a and Ma have associated with'them pressure rolls l3a and Ida respectively, for keeping'the strip in close contact with the guide rolls,

That portion ofthe strip between roll [3a and roll Ma is electric resistance heated bypassing current through the strip from one roll to the o.ther, and the construction of and electrical connections to the rolls l3a and Ma are substantially identical, so that only roll I3a is shown in cross section in Fig. 3. Rolls l3a and 14a are constructed of good current conducting material such as copper with a hard polished outer surface such as'chrome plate.

"Referring to Fig. 3, roll 13a is preferably a hollow cylinder closed at both ends by end walls 55, through which is inserted a hollow shaft '56. One end of the shaft 56 is connected with a source of cooling fluid which passes from the inside of the shaft through a slotted opening 5'! therein at one side of the partition wall 53 and into the roll to cool the same. The cooling fluid is withdrawn from the roll through a slotted opening 59 on the other side of partition 58 and discharges out of. the other end of the shaft.

' Preferably, the shaft 56 is journaled in'bearings .66 outside the compartment walls,,and the shaft is sealed as indicated at El where it passes through said walls. At one side of the chamber, the shaft has mounted thereon a current collecting drum 62 slidablyengaged by electric brushes 63 connected'by conductor 64 to one side of a generator '65. The other side of the generator is similarly connected by conductor 66 to the current conducting roll 14a.

Suflicient current from generator 65 is passed through the strip between rolls I3a and [4a to raise the temperature of the tin coating above its melting point before the strip reaches partition 29 through which it passes into the quenching compartment. In the quenching compartment the strip surface is immediately cooled by sprays or jets 3!! to a temperature below the solidification point of the tin, that is 425 F. or less, before the strip contacts roll I4a.

Referring to Fig. 4, the strip in passing through the second preheating compartment B is heated to approximately 440 F. by contact with the heat conducting medium circulated in said compartment and maintained at required temperature.

The strip passes over guide roll l3 and then through a high frequency induction coil 68 connected to a conventional source of high frequency current such as a tube oscillator set and so constructed and arranged that the current passing through the coil substantially instantaneously raises the temperature of the strip to about 460 F. to fuse the tin coating thereon. Thus, the fusing zone C is located above the liquid level L in this embodiment of the invention.

On leaving the coil 63, the strip passes immediately into a body of heat conducting medium in compartment C, which may be termed the first quenching zone, and a circulation pipe 59 is especially provided for connecting the upper part of the medium in compartment C with the upper part of the medium in compartment A, so that part of the heat taken up from the strip is transferred to the incoming portion S of the strip 7. and the temperatures of the medium in compartments C and A are substantially equalized.

The strip then passes through partition 29 and into a second quenching zone whenitis sprayed at 30 by cooled liquid 'medium to insure that the coating is cooled to below 425 F. before the strip contacts the guide'roll l4 so that the finish on the coating is not marred.

As the strip passes under guide-roll l5 and upward as shown at S! in Fig. 4, it Willcontinue to give up heat to the liquid medium in compartment A, which heat will be partly absorbed by the incoming strip S until a balance of heat transfer between the outgoing and incoming parts of the strip is effected;

In the embodiments of the invention shown in Figs. 2 and 4, the strip leaving compartment A is preferably treated as shown to reduce and control the amount of film of heat transfer medium left on its surfaces. As shown, the apparatus and method of treatment for controlling said film may be the same as described in connection with Fig. 1. However, for certain purposes the strip leaving the heat transfer compartment A may be suitable without further treatment.

To cite specific examples by way of comparison, assume that the incoming strip S in the apparatus shown in Figs. 1, 2 and 4 is at a temperature of 150 F., the heat treating medium at the top of compartment A where the strip enters the same at about350 F., and at roll [2 and at the suction pipe H5 in compartment B about 300 F.; also assume that the discharge at sprays 2! is about 447 F., and the heater [9 to be gas fired with gas atl000 B. t. u. per cubic foot at $.43 per 1000 cubic foot, and assume the apparatus to be built so that in compartment B the incoming strip temperature will be raised from 300 F. to 440 F. and iii-compartment C from 440 F. to 460 F. and the heating efliciency of the gas is In the apparatus of Fig. 1, the cost of heating is as follows:

2000X .l2(460300) X .43 1000 X 1000 X .50

in which .12 is the specific heat of steel.

If the heat transferred from the strip to the heat transfer medium in .the quenching zone is not reclaimed and used to preheat the incoming strip, the cost would be ZOOOX .12(460'150) X .43 1000X 1000X.50

In the apparatus of Fig. 2, the cost of ,preheating is 2000X .12(440-300) X .43 lOOOX 1000X .50

And the cost of fusing the coating by resistance heating, in which the heat generated in the strip is equal to the current squared times the strip resistance times the time of current flow. (I R=watts.) The heat generated in the strip below the surface of the quenching medium will be an added loss, therefore assume the proportion of we strip under the quenching medium to be such that the heat generated under the surface of the medium is /4 of the total heat generated by electric resistance. Assume that the cost of electricity is $006 per k. w. h. with an efficiency for resistance heating of approximately 85%. The cost of heating the strip for fusing by resistance heating is =$.063/ton =$.029/ton.

In the apparatus of Fig. 4, the cost of preheating is $.029 plus the cost of the electricity for fusing by high frequency, which is so that the total cost is $.02!) plus $.018, or $.04? per :ton.

Thus, the method carried out in the apparatus of Fig". l is the cheapest, but this method is limited as to strip speed because the greater the; strip speed the smaller the temperature dilference is between the strip and the heat transfer medium. Thus, for high strip speeds, the preheating chambers and particularly the fusing chamber must be relatively long.

While the cost of using high frequency current is relatively high, by using it for fusing only as in Fig. 4, it is only necessary to raise the strip temperature from 440 F. to 460 F., or about 20 and the strip is heated very quickly in a short space without making physical contact with the strip, making possible very high strip speeds with small additional operation cost and without high expense for installing heavy high frequency heating equipment for heating over a much larger temperature range.

In the. modified form of the invention shown in Fig. 5, the apparatus is generally similar to that of Fig. 1 in respect to the heat transfer, preheat,v fusing and quenching zones and the samereference numerals are applied to the same or similar parts thereof. The apparatus of Fig. 5 differs from that of Fig. l in providin further novel means for coordinating the drying and preheating of the incoming strip with the control of the-film of heat transfer medium left on the outgoing strip S so as to further reduce the over all cost of operation.

After the strip S leaves the heat transfer compartment A, it passes between squeegee rolls 33a and 34a; and then through a series of hot air jets 10 located above and below the strip and adapted for directing hot air against the strip at anangle and counter to the direction of the strip travel. The air is heated in a conventional manner preferably to a temperature of about 300 F. or below the oxidation point of the tin coating and is circulated to the jets 10 through pipes H to the jets.

As shown, a hood i2 is provided for enclosing the rolls 33a and 34a, as well as guide roll lid and a. substantial portion of the incoming strip S ahead of roll Ha, so that the heated air from jets l0 flows over the incoming strip to dry and preheat the same before it reaches the heat transfer medium in compartment A. Preferably means such as an exhaust fan 13 is provided at the: entrance end of hood [2, in order to create a minus pressure Within the hood, which I have found increases the rate of evaporation on the incoming strip surface.

With the arrangement of Fig. 5, the conventional drier used before heat treating the strip may be omitted, and the strip after being electroplated may be rinsed w'ith hot water and passed through squeegee rolls for removing excess water and then directly into the hood I2 where the remaining moisture will be removed by the heated air flowing along the strip in the opposite direction to the strip travel.

The film of heat transfer medium left on the outgoing strip S after it passes through rolls 33a and 34a will be largely taken up by the heated air enterin through jets I0, and further economies may be efiected by using this mixture of air and heat transfer medium as a combustible mixture for feeding gas burners which may in some cases be used for maintaining the heat transfer medium in compartments B or C at the required temperature.

In the modified form of the invention shown in Fig. 6, the apparatus includes outer walls forming a brightening tank with inner preferably vertical partition walls 16, TI and I8 dividing the tank into preheating, fusing, quenching and cooling chambers. Chamber A may be called a first preheating chamber, chamber B the second preheating chamber, chamber C fusing, chamber C quenching, and chamber C" cooling. A circulation pipe 19 provides communication between the upper parts of chambers C" and A so that part of the heat taken up from the portion S" of the strip by the medium in chamber C" is transferred to the incoming portion S of the strip in chamber A and the temperatures of the medium in said chambers are substantially equalized.

After being electroplated and rinsed, the strip S enters the elongated hood 80, through which hot air is circulated from a heater 8| over the outgoing strip S" to an exhaust fan 82, as indicated by the arrows in Fig. 6. This heated air contains some heat transfer medium which has been taken up by the air in passing over the outgoing strip, and the mixture dries and preheats the incoming strip to about 150 F. or more, so that the use of a conventional drier prior to the brightening treatment is not necessary.

The incoming strip passes over a guide roll 83 within the hood and then downward into the first preheating chamber A, which at its lower end communicates as shown with the quenching chamber or zone C. At the lower end of preheat chamber A, the strip passes under a guide roll 84 and then upward through a partition wall 85 and into a second preheat chamber B, which is provided with a circulation. system including pump 86, filter 81, heater 88 and sprays 89 for recirculating and heating the medium in said chamber,

In passing through the first preheating chamber A, the strip is heated to approximately 300 F., and in passing through the second preheat chamber B, the strip temperature is raised to approximately 440 F.

On leaving the chamber B, the strip passes over an upper guide roll 90, which is preferably enclosed by a rounded hood 9| within the elongated hood 80, and the rounded hood 9| is preferably provided with a pressure relief pipe 92 leading to a condensing and return unit (not shown) such as indicated at 50, 52 and 53 in Fig. l, for relieving the pressure built'up within the hood 9| by vaporization of the heat transfer medium.

From the guide roll 90, the strip passes downward through a fusing chamber C in which the heat transfer medium is maintained at a temperature sufiicient to raise the temperature of the tin coating from 440 to 460 F. to melt and flow the tin. Preferably, a recirculating and heating system is provided for the medium in chamber C and includes a pump 93, filter 94, heater 95 and spray 96.

From the fusing chamber C, the strip passes downward through partition 85 and into the quenching zone C, which communicates with the lower part of the first preheat chamber A, and in the quenching zone the strip is cooled by sprays 9! discharging heat transfer medium circulated from the bottom of chamber A by pump 98 for cooling the tin coating to about 425 F. to set and solidify the tin coating.

From the quenching zone C, the strip passes downwardly through a partition 99, which connects the outer wall 15 of the first preheat chamber with the vertical partition wall 18, and then under a guide roll I 00 located in the lower part of the cooling chamber C. The outgoing strip S" passes upwardly from guide roll I00 through the cooling chamber C, which is filled as shown with heat transfer medium, and then between squeegee rolls Hll and iilla within the hood 80 and through a partition wall 102 into a chamber G wherein the amount of film of medium on the strip is controlled.

In the chamber G the strip passes through sets of squeegee rolls 103 for removing part of the film and further amounts of the film are taken up by the heated" air circulated through chamber G by the fan I04, which moves air through the heater 8| into the chamber. The mixture of heated air and medium is circulated from chamber G through partition wall" I 02 and through the hood 80 around the incoming strip S to the exhaust fan 82. Preferably, the fan 82 is arranged to withdraw air from chamber G at a rate which will create a minus or reduced pressure in the chamber, in order to increase the rate of evaporation of the film on the strip passing through said chamber.

From the chamber G the strip passes through a partition wall 105 into a chamber F, in which the strip passes between cooling rolls I05 to stop further evaporation of the oil and leave an imperceptible film on the strip to facilitate further operations such as forming or drawing the same.

The oil bath used as a liquid medium in compartments A, B and C, in each of the forms of the invention is preferably as stated, a bath of a high boiling petroleum fraction having a final boiling point range between the approximate limits of 450 F. and 850 F. A typical petroleum fraction having a boiling point range within the range referred to is a material sold under the trade name of Mentor 28 which has a boiling point range of 505 F. to 650 F., a flash point of approximately 255 F., and a fire point of approximately 294 F. This material has a Viscosity of 4.83 centipoises at 25 C., has practical- 1y no vapor pressure or evaporation loss at 25 C., and a gravity range between 35 to 38 A. P. I.

Another typical petroleum fraction is a material sold under the trade name of Mineral Seal Oil VM-1103, which has a boiling point range offrom 530 F. to 650 F., a fiash point of 260 F. to 270 F., a Viscosity of 4.6 centipoises at F., substantially no vapor pressure or evaporation loss at room temperature, and a gravity range between 36 and 37 A. P. I.

, These materials are non-oxidizing in character with reference to the tin on the strip steel and the tin coated strip throughout the bright-- ening process is maintained under non-oxidizing conditions because it is either immersed in the oil bath or passes through a closed chamber filled with vapors from the oil bath, or is coated with. a .film of the.,oil. .Moreover, these mate.-v

11 rials within the range referred to have a high rate of heat transfer.

Thus, the use of the particular petroleum fractions Within the range specified provides special advantages and results in that the high rate of heat transfer enables the operations to be rapidly carried out and the particular petroleum fractions may be used for the final surface preparation of the strip in accordance with the inventions set forth in my copening application Serial No. 484,722, thus eliminating the necessity of removing the oil from the surface at the conclusion of the brightening operation.

In this connection, although it has been pointed out that gas may be used in the heaters for heating the oil in compartments B and C, electric heaters or oil burners could also be used, s being preferable in the interest of economy.

In the brightening of electro tin plate by melting the tin, the tin cannot be contacted by solid objects such as rolls While molten. Therefore, in order to keep the size of the fusion compartments C as small or as short as possible, it is desirable to have the temperature of the heating medium as high as possible so as to reduce the time of fusion and the size of the apparatus. The limits of maximum temperature used are of course determined by the type of heating medium; and electric induction heating or electric resistance heating enables a shorter fusion zone to be used than when the fusion is carried out solely in an oil bath.

In modern high speed electrotinning lines the line speed is frequently reduced at the time a new coil is welded to the trailing end of the previous coil. In the fusion zone, the length of the zone and the temperature of the heating me dium should be such .that at the maximum line speed, the tin will melt, and at minimum line speed the tin-iron alloy formed will not be of such magnitude as to give trouble in deep drawing operations of the finished product. The time limits in which tin can be ina molten state on a steel base andyet provide a good tin plate for wet packs in cans, is from one second to approximately sixty seconds. If the tin coating is melted and held in the molten state too long, the tin tends to pull into small beads or to have a surface known .as "orange peel. Too short a time in the moltenstate will not give a good bond between the tin and the steel base.

Therefore, in the last preheating step, the temperature of the strip and tin should not exceed 440 F., but the preheat medium may be of a higher temperature than 440 F. Since variations in the line speed will result in variations in the time of preheating, if the preheat medium is above tin melting temperature, then the tin will melt in the preheat zone if the line speed is reduced to a minimum for too long a time and the strip maybe spoiled. This situation may be controlled and the tin prevented from being .melted in the preheatzone when the line speed is slowed down by varying the temperature of the strip as it enters the preheatzones.

For example, at full line peed the drier may be operated to deliver heated air to the strip at such a rate that the strip temperature will be somewhere between 240 F. to 250 F. If theline speed is reduced, the temperature of the drier and the rate of air fiow is automatically reduced so as to reduce the initial temperature of the strip. This automatic control may be accomplished by conventional devices such as opening cold air vents or reducing fan speeds; and as. the

12 line speed is again accelerated the drier temperature is raised automatically so that the strip enters the preheat zones at a temperature which will again permit the preheat medium to raise the temperature to approximately 440 F.

Accordingly, the present invention provides for saving heat energy and increasing overall efficiency in carrying out a brightening operation, provides for controlling the preheating temperature by controlling the initial strip temperature, provides an improved heat transfer medium, furthur contributing to loW cost operation and increased efficiency and provides for utilizing the heat of controlling the final film on the strip to initially dry or preheat the material.

Having now described the features of the invention and the advantageous new results attained by the improved method and apparatus; the new and useful methods, steps, arrangements, coordination, apparatus and combinations, and reasonable mechanical equivalents thereof obvious to those skilled in the art, are set forth in the appended claims.

I claim:

1. The method of continuously brightening steel :strip electroplated with tin which includes the step of preheating the strip by passing the strip through a first body of liquid hydrocarbon heat conducting medium maintained at a temperature sufficient to preheat the tin to just below its melting point, then raising the temperature of the tin sufficiently to melt the tin while passing the strip through a zone containing a second body of liquid hydrocarbon medium, then quenching the tin by passing the strip through a third body of liquid hydrocarbon medium maintained at a temperature which will quench and solidify the tin, said bodies of heat conducting medium being in communication with each other for passage of the strip therebetwcen, and introducingrthe strip on its way to the first preheating body of medium through said third quenching body of medium "in heat exchange relation therethrough with the quenched strip so as to utilize the heat absorbed by the quenching medium from the quenched .strip to heat the incoming strip.

2. The method of continuously brightening steel strip electroplated with tin which includes the steps of preheating the strip by passing the strip through a first body of liquid hydrocarbon heat conducting medium maintained at a temperature suflicient to preheat the tin to just below its melting'point, then raising the temperature of the tin sufficiently to melt the tin while passing the strip through a zone containing a second body of the same medium, then quenching the strip by passing the strip through a third body of the "same medium maintained at a temperature which will quench and solidify the tin, said bodies of heat conducting medium being in communication with each other for passage of the strip therebetween, and introducing the strip on its way to the first preheating body of medium'through said third quenching body of medium in heat'exchange relation therethrough with the quenched strip so as to transfer heat from the quenched strip to the incoming strip.

.3. The method of continuously brightening steel strip electroplated with tin which includes the step of preheating the strip by passing the strip through a first body of heat conducting medium maintained at a temperature sufficient to preheat the tin to just below its melting point, then raising-the-temperature of the tin sufficient; 1y to melt the tin while passing the strip through a zone containing a second body of medium, then quenching the tin by passing the strip through a third body of medium maintained at a temperature which will quench and solidify the tin, said bodies of heat conducting medium being in communication with each other for passage of the strip therebetween, and introducing the strip on its way to the first preheating body of medium through said third quenching *body of medium in heat exchange relation therethrough with the quenched strip so as to transferheat from the quenched strip to the incoming strip, said heat conducting medium bodies each being a liquid hydrocarbon body comprising a petroleum fraction having a final boiling point range between the approximate limits of 450 F. and 850 F.

4. The method of continuously brightening steel strip electroplated with tin which includes the steps of preheatin the strip by passing the strip through a first body of liquid hydrocarbon heat conducting medium maintained at a temperature sufficient to preheat the tin to about 440 F., then raising the temperature of the tin to about 460 F. while passing the strip through a zone containing a second body of liquid hydrocarbon medium, then quenching the strip by passing the strip through a third body of liquid hydrocarbon medium, and introducing the strip on its way to the first preheating body of medium through said third quenching body of liquid hydrocarbon medium in heat exchange relation therethrough with the quenched strip, so as to transfer heat from the quenched strip to the incoming strip through the liquid hydrocarbon whereby the quenched strip emerges from the third body at about 310 F. and the incoming strip is heated to a temperature of about 300 F. in said third body.

5. The method of continuously brightening steel strip electroplated with tin which includes the step of preheating the strip by passing the strip through a first bod of liquid hydrocarbon heat conducting medium, then further heating the strip by passin the strip through a second body of liquid hydrocarbon heat conducting medium maintained at a temperature suflicient to preheat the tin to just below its melting point, then raising the temperature of the tin sufiiciently to melt the tin, then quenching the strip by passing the strip again through the first body of said medium to solidify the tin, said bodies of heat conducting medium being in communication with each other for passage of the strip therebetween and passing the quenched strip through said first preheating medium body in a direction opposite to that in which the incoming strip passes through said body.

6. In a method of continuously brightening steel strip electroplated with tin, the steps of passing the strip through a, petroleum fraction having a final boiling point range between the approximate limits of 450 F. and 850 F. to preheat the tin, then raising the temperature of the tin to melt the tin, then quenching the strip to solidify the tin and passing the quenched strip through said petroleum fraction to transfer heat to the incoming strip, said preheating, melting and quenching zones being in communication with each other for passage of the strip therebetween circulating heated air over said quenched strip to evaporate some of the film on the surface of the strip, and directing said circulated heated air along the incoming strip on its way to said preheating petroleum fraction.

7. In a method of continuously brightening steel strip electroplated 'with tin, .the steps of passing the strip through a petroleum fraction having a final boiling'point range between the approximate limits of 450 F. and 850 F. to preheat the strip,'then raising the temperature of the tin to melt the tin then quenching the strip by passing the strip through said petroleum fraction to solidify thetinand to transfer heat to the incoming'strip, said preheating, melting and quenching zones being in communication with each other for passage of the strip therebetween,

then passing said quenched strip through heated gaseous fluid to control the oil film thereof, and circulating the gaseous fiuid around said incoming strip before said strip enters the preheating petroleum fraction.

8. In a method of continuously brightening steel strip electroplated with tin in which the strip is preheated and quenched in a bath con sisting of a petroleum fraction having a final boiling point range between the approximate limits of 450 F. and 850 F., the steps of controlling the film on the surface of the strip by passing the strip through heated air to evaporate some of the film, as the strip emerges from the bath, and then circulating the heated air around the incoming strip to initially preheat the strip before the strip enters the bath.

9. Apparatus for continuously brightening strip electroplated with tin including walls forming a tank for containing heat transfer liquid, partition walls dividing said tank into communicating first and second preheating zones, a fusing zone, and a quenching zone, means for moving the strip successively through said first preheating zone, second preheating zone, fusing zone and quenching zone, means for controlling the temperatures of the heat transfer liquid in the various zones, and said first preheating zone communicating with said quenching zone whereby heat absorbed by the medium in said quenching zone will be transferred to the strip in said first preheating zone.

-10. Apparatus for continuously brightening strip electroplated with tin including walls forming a tank for containing heat transfer liquid, partition walls dividing said tank into communicating first and second p eheating zones, a fusing zone, and a quenching zone located below said fusing zone, means for moving the strip successively through said first preheating zone, second preheating zone, fusin zone and quenching zone, means for controlling the temperatures of the heat transfer liquid in the various zones, and means for passing the strip from the quenching zone through said first preheating zone whereby heat from the quenched strip is transferred through said medium to the incoming strip passing through said first preheating zone.

11. Apparatus for continuously brightening strip electroplated with tin including walls forming a tank for containing heat transfer liquid hydocarhon, partition walls dividing said tank into communicating first and second preheating zones, a fusing zone, and a quenching zone located below said fusing zone, means for moving the strip successively through said first preheating zone, second preheating zone, fusing zone and quenching zone, means for controlling the temperatures of the heat transfer liquid in the various zones, and means for passing the strip from the quenching zone through said first preheating zone in the opposite direction to the incoming strip passing through said first preheating zone whereby heat is transferred from the 15 quenched strip to said incoming strip by means Number of the liquid hydrocarbon medium. 2,240,265 JOHN'S. NACHTMAN. 2,274,963 2,303,035 REFERENCES CITED 5 2 324 359 The following referencesare of record in the 2,357,126

of this patent:

UNITED STATES PATENTS Number Number Name Date 10 457,780 2,009,856 Otis July so, 1935 639,701 2,192,303 Ferm Mar. 5, 1940 Name Date Nachtman Apr. 29, 1941 Hopper Mar. 3, 1942 Fink Nov. 24, 1942 Macan July 20, 1943 Na-chtman Aug. 29, 1944 FOREIGN PATENTS Country Date Great Britain Apr. 29, 1936 France Mar. 17, 1928 

